This invention relates generally to the field of solar energy conversion and more particularly to a concentrating solar energy receiver.
Devices for solar energy collection and conversion can be classified into concentrating types and non-concentrating types. Non-concentrating types intercept parallel unconcentrated rays of the sun with an array of detection or receiving devices such as a solar panel of photovoltaic cells or hot water pipes, for example. The output is a direct function of the area of the array. A concentrating type of solar energy collector focuses the energy rays using, e.g., a parabolic reflector or a lens assembly to concentrate the rays, creating a more intense beam of energy. The beam is concentrated to improve the efficiency of conversion of solar radiation to electricity or to increase the amount of heat energy collected from the solar radiation to provide for heating of water and so forth. In a conventional concentrating solar energy receiver, the incident solar radiation is typically focused at a point from a circular reflector (e.g., a dish-shaped reflector) or along a focal line from a cylindrical shaped reflector. In another prior art example, such as disclosed in U.S. Pat. No. 5,882,434 issued to William E. Horne, a flat portion in the center of a round, parabolic primary reflector provided by flattening the center portion of the reflector radially to a predetermined diameter before the parabolic curve commences outward to the rim of the reflector. In this device the reflected solar energy is focused at a ring corresponding to the outer diameter of the flat central portion of the reflector.
However, even conventional concentrating solar energy receivers require improvement for two reasons. First, the solar energy conversion module in conventional systems is located directly at the focal point or focal line which occupies a very small volume. This small volume causes a high concentration of heat that must be dissipated in the region of the focal point. Secondly, a large portion of the infrared portion of the radiant solar energy spectrum cannot be efficiently converted to electricity by currently available low mass conversion devices such as solar cells. Instead, this excess infrared energy is collected by the reflector and contributes to heating the conversion device which can impair the conversion efficiency of the solar cells.
There is disclosed herein a concentrating solar energy receiver comprising a primary parabolic reflector having a high reflectivity surface on a concave side of the reflector and having a focal axis extending from the concave side of the reflector which passes through a focal point of the primary parabolic reflector; and a conversion module having a reception surface wherein the reception surface is spaced from the focal point by a predetermined distance and disposed to receive a predetermined cross section of radiant solar energy reflected from the concave side of the primary parabolic reflector. The radiant energy thus collected may be converted to electrical energy in the conversion module. In one aspect, the conversion module includes a reception surface comprising a planar array of at least one photovoltaic solar cell. In another aspect, the conversion module includes a reception surface coupled to a thermal cycle engine. The mechanical output of the thermal cycle engine drives an electric generator.
In an alternate embodiment, there is disclosed a concentrating solar energy receiver comprising a primary parabolic reflector having high reflectivity surface on a concave side of the reflector and having a first focal axis extending from a concave side of the reflector which passes through a focal point of the primary parabolic reflector; a secondary parabolic reflector of smaller area than the primary parabolic reflector which has a second focal axis aligned along the first focal axis, and is disposed with a convex side having a high reflectivity surface facing the concave side of the primary parabolic reflector. The secondary parabolic reflector is spaced from the focal point of the primary parabolic reflector along the first focal axis by a predetermined distance, for reflecting the radiant solar energy reflected from the primary parabolic reflector, in substantially parallel rays, toward a central portion of the primary parabolic reflector. A conversion module, having a reception surface wherein the reception surface is positioned along the first focal axis within the central portion of the primary parabolic reflector is disposed to receive the radiant solar energy reflected from the secondary parabolic reflector. The radiant energy thus collected may be converted to electrical energy. In one aspect, the concentrating solar energy receiver is configured to selectively admit the radiant solar energy to the conversion module such that an admittance bandpass of the system to the radiant solar energy substantially matches a conversion bandpass of the conversion module. In another aspect, the conversion module includes a reception surface which comprises a planar array of at least one photovoltaic solar cell. In yet another aspect, the conversion module includes a reception surface coupled to a thermal cycle engine. The mechanical output of the thermal cycle engine drives an electric generator.